Mexico claims that instability is caused by U.S. demand for lucrative and illegal narcotics.

Secretary of State Clinton addressed that claim...

"We know that the demand for drugs drives much of this illicit trade, that guns purchased in the United States, as we saw some of the examples outside, are used to facilitate violence here in Mexico, and the United States must.
We have watched with great grief the terrible tragedies and murders that have taken place here in Mexico, and then our hearts were broken by the murders in Juarez which took the lives of three people connected to our Consulate. They were but the latest, horrible reminder of how much we have to do together."